The present invention relates to improvements to wings fitted to waterborne or airborne vehicles by enabling automatic and linked progressive variation of the camber and the angle of attack of the wing, depending on the direction and relative velocity of the fluid.
To limit or instigate the lateral displacement of a vehicle an effective force called hydrodynamic or aerodynamic lift is usually produced by a wing or hydrofoil. The useful lift force produced by this wing is accompanied by an undesirable force, called drag, which opposes the progress of the vehicle. The wing's profile is crossed by a line named the chord, connecting the leading edge to the trailing edge. The profile is said to be cambered, following a curved line, if it is asymmetric about the chord. The angle of attack of the wing is the angle between the chord and the direction of the fluid. It is well known that the lift and drag forces increase as the angle of attack is increased. It is also well known that for profiles of identical thickness and angle of attack, a cambered profile creates more lift and drag than a profile with a camber of zero and that is symmetrical about its chord.
This efficiency gain provided by the camber is explained by the speed difference and distance traveled by the fluid between the lower and upper surfaces of the profile which, according to Bernoulli's well-known equation, generates a pressure difference between the lower and upper surfaces of the profile It is also well known from the physical law of the change of momentum, that the change in direction of the fluid created by the profile generates a beneficial reaction force when the trailing edge is aligned with the direction of the force that it is desired to produce. (References to aerodynamics: “The element of wing and airscrew theory” by H. Glauert, “Subsonic aerodynamics (aérodynamique subsonique)” by Ion Paraschivoiu, École Polytechnique de Montréal, 1998).
As a result, for minimum drag, it is best to have a symmetrical profile with zero camber and a zero angle of attack and, to obtain lift, apply an angle of attack or a camber to the profile, or both together.
When a boat is not subjected to lateral forces and is moving in the right direction, the centreboard should not generate any lift and should produce the minimum of drag. In these conditions, where the required lift force is zero, the optimum profile will have a zero angle of attack and no camber. But when a lateral force applied to the vessel drags the boat sideways in one direction, the profile's angle of attack and camber must be modified to generate a lift force designed to limit the sideslip as far as possible.
The result of these variations in the lift requirements is that, to obtain optimum performance under varying conditions of lateral movement the camber must be varied in conjunction with varying the angle of attack, to change from a camber of zero (yielding a symmetric profile when the angle of attack is zero) to a maximum camber when the angle of attack is a maximum. Traditional centreboard or rudder profiles have the disadvantage of not varying their camber with the angle of attack, resulting in sub-optimal performance.
Another parameter limiting the performance of profiles with traditional designs is that the optimum angle of attack and the orientation of the leading edge is difficult for the manufacturer to assess, as they have to precisely locate the centreboard in a watercraft operating in conditions of continuously varying fluid speeds and directions. This results in performance losses arising from excessive or insufficient angles of attack and badly aligned leading and trailing edges, when the direction and speed of the vehicle varies. This is a disadvantage for traditional anti-drift devices.
Devices for adjusting the shapes and angles of attack of sails are well-known, but these devices require human intervention for their adjustment.
Flexible wings with adjustable or invertible cambers are well known but these devices do not allow progressive and simultaneous variation of the camber and the angle of attack depending on the lateral force.
It is well known from patents FR 2 654 063, FR 2 643 328 and FR 267 775 which disclose ailerons with adjustable flaps modifying the profile's camber, or devices for varying the shape of profiles disclosed in WO 2014/118749 but these devices do not change their camber in conjunction with their angle of attack, and the direction of the leading edge is not automatically adjusted to correspond with the lateral force. This results in manual interventions and adjustments that are difficult to envisage in conditions in which there are frequent variations in direction.
Devices incorporating wings with angles of attack that vary as a function of the transverse force are well known, but are devoid of any variation of camber, such as the devices disclosed by patent FR 2 903 377 relative to flippers, but without the camber being linked to the angle of attack the wing's trailing edge does not allow optimum redirection of the fluid leas it leaves the wing and this limits performance.
Also well known, disclosed in patent DE 36 19 998, is a device consisting of a deformable wing elastically connected to two parallel shafts. These are connected by two rigid arms. The two shafts and the arms form a non-deformable quadrilateral.
Patent DE 36 19 962 also discloses a device consisting of a deformable wing elastically connected to two shafts. One of the shafts is connected at each of its ends to the two rigid arms, while the other shaft is connected to a bracket consisting of two fixing lugs. These two fixing lugs are further connected to an additional shaft, the latter being connected to the two rigid arms described previously.